Microelectromechanical systems (MEMS) have recently been developed as alternatives for conventional electromechanical devices such as relays, actuators, valves and sensors. MEMS fabrication allows the coupling of mechanical and electronic functionality in a single micro-scale device. Borrowing from integrated circuit fabrication, MEMS processes are typically performed on silicon wafers using batch processing techniques. This permits greater economies of scale, higher precision, and better device matching capabilities than conventional assembly-based manufacturing. New functionality may also be provided because MEMS devices are much smaller than conventional electromechanical devices.
One of the components of a mechanical relay is the actuator used to close or open the switch contacts. Common MEMS actuators are driven by electrostatic or electrothermal forces.
D. Bosch et al., xe2x80x9cA Silicon Microvalve with Combined Electromagnetic/Electrostatic Actuation,xe2x80x9d Sensors and Actuators, 37-38 (1993) 684-692, describes a silicon microvalve that uses a combination of electrostatic and electromagnetic actuation. The valve consists of two micromachined components which are then bonded together. Because the two micromachined components are bonded together, increased complexity in assembly is introduced which could lead to errors in alignment of the two parts.
It is desirable to provide a microrelay that has high contact-to-contact isolation when the relay is in the OFF state to increase relay performance. It is also important to provide a microrelay with very low contact resistance and negligible power dissipation when the microrelay is in the ON state to increase relay lifetime and reliability. Also, it is critical to provide a microrelay that requires minimal assembly and lends itself to batch fabrication techniques to reduce product cost. In addition, it is desirable to provide a microrelay that has reduced actuation currents and voltages to reduce device power and lessen heat generation.
According to a first aspect of the invention, there is provided a microelectromechanical relay. The relay has a substrate layer having a trench formed therein. A first pair of contacts and the bottom electrode are located in the trench of the substrate and a microelectromechanical actuator and contact bar are located on the substrate for controllably establishing electrical contact between the first pair of contacts on the substrate. The actuator includes spaced apart anchors on the substrate, a movable beam extending between the spaced apart supports, a contact cross bar located on the movable beam, the contact cross bar facing the first pair of contacts, means for deflecting the movable beam towards the first pair of contacts on the substrate, and means for bringing the cross bar in physical contact with the first pair of contracts.
According to a second aspect of the invention, there is provided a microelectromechanical relay. The relay includes a substrate having a trench formed therein. A first pair of contacts is located in the trench of the substrate and a microelectromechanical actuator is located on the substrate for controllably establishing electrical contact between the first pair of contacts on the substrate. The actuator includes spaced apart supports on the substrate, a movable beam extending between the spaced apart supports, a contact cross bar located on the movable beam, the contact cross bar facing the first pair of contacts, means for generating an electromagnetic (Lorentz) force on the movable beam to deflect the beam towards the substrate, and means for generating an electrostatic force between the beam and the substrate so that the contact cross bar is brought into physical contact with the first pair of contacts.
According to a third aspect of the invention, there is provided a microrelay that includes a first electrode located on the movable beam and a second electrode located on the substrate. The first electrode is at a different potential than the second electrode so that when the first and second electrodes are brought into close proximity to one another, an electrostatic force is generated therebetween to bring the contact cross bar in contact with the first pair of electrodes. Also included are current carrying coils located in the movable beam wherein when the relay is placed in a permanent magnetic field, an electromagnetic force is exerted on the movable beam to deflect the beam towards the pair of contacts close enough so that the electrostatic force takes over.
According to a fourth aspect of the invention, there is provided a method of fabricating a microelectromechanical relay. The method includes the steps of:
(a) etching a deep trench anisotropically into a silicon substrate;
(b) depositing an insulating film on the entire surface of the substrate;
(c) depositing a conductive film on the insulating film;
(d) etching away the conductive film deposited in step (c) to create a pair of contacts and an electrode in the deep trench;
(e) filling deep trench with a sacrificial material;
(f) polishing the substrate to create a flat surface;
(g) creating a beam layer over the deep trench; and
(h) removing the sacrificial material.